The purpose of this project is to identify, primarily by two-dimensional gel electrophoresis, polypeptides that characterize the cell surface in normal neoplastic cells. Studies on normal hepatocytes from rats at different stages of development and from regenerating livers will be compared to studies preneoplastic and neoplastic liver cell populations in order to identify alterations in cell surface polypeptide patterns that distinguish the malignant cell from the normal cell. (1) We have compared three methods for cell surface protein radioiodination and have further refined one of these methods to yield high resolution, low background two-dimensional gel electrophoresis autoradiograms after a short exposure. Presumptive cell surface protein patterns of rat hepatocytes and of two rat hepatoma cell lines are currently being compared by computer analysis. (2) We are in the second phase of development of a medium designed to support the growth of rat hepatocytes under hormone-supplemented serum-free conditions.